Abstract Core A: The Physics Core is responsible for providing and maintaining PDT laser sources, for in vivo and ex vivo light dosimetry, for quality assurance of light delivery systems, and for establishment of absolute light dosimetry standards traceable to NIST. It implements useful technologies to routine clinical application. The Physics Core is responsible for providing laser support and in vivo light dosimetry for all projects. It works with Project 1 to develop human clinical trials for treatment of pleural disease. The core supports maintenance and operation of the lasers housed in the 8th floor of the Smilow Center for Translational Research (SCTR 8W) that will be used for the cell and mouse PDT experiments included in Projects 2, 3 and 4. All of these illuminations will be performed through the services of the Animal/Pathology Core with assistance from the Physics Core as needed. In addition, the Physics Core will perform an annual on-site visit for dosimetry calibration at Roswell Park Cancer Institute (RPCI) and will remotely perform quarterly reviews of the light dosimetry data from RPCI via email submission. The Physics Core will develop techniques to improve PDT dosimetry for human clinical trials to achieve better uniformity of light fluence distribution. Determination of tissue optical properties, blood flow, sensitizer distribution, and tissue oxygenation for individual patients may prove to be important in providing individualized treatment planning and thus improving cancer treatment. The major components of the Physics Core can be summarized as follows: 1) to provide maintenance and operation of laser and light sources for PDT; 2) performance of in vivo and ex vivo light dosimetry; 3) measurement of absolute light dosimetry; 4) support for light dosimetry at RPCI and 5) to perform explicit PDT dosimetry for tissue optical properties, drug concentration, and tissue oxygenation before, during, and after PDT.